1. Field of the invention
The invention relates to a network for transmitting information signals between stations connected to that network, which is provided with a number of switching devices and a number of transmission sections, which switching devices can switch on, switch over or switch off parts of the network or stations connected to the network by means of control signals, and which transmission sections achieve the transmission of information signals between one switching device and another respectively between the switching devices and the stations connected to the network, for which purpose the information signals are supplied to those transmission sections on one side of them, and are separated on the other side of them, and which transmission sections comprise one or more parallel optical conductors (e.g. glass fibres), at least part of the number of transmission sections moreover achieving the transmission of said control signals to the switching devices, for which purpose in the relevant transmission sections also the control signals are supplied to those transmission sections on one side of them and are separated on the other side of them, the transmission of said signals in the transmission sections at taking place at least substantially in the optical domain.
2. State of the art
A network as mentioned above is known from "TELEPHONY" of April 15, 1985 [1], notably pp. 60-64, in which various network configurations are described, formed substantially formed by transmission sections and switching devices. External stations (hosts) can be connected--via transmission sections--to the network, which stations can then interchange information signals via the network. The transmission section which has come from a suchlike station is connected to a switching device, which is connected to the rest of the network, in this case to other switching devices, via further transmission sections. The switching device has the function either to connect the latter transmission sections to one another and to close in itself at the same time the transmission section coming from the host (first switching state), or to insert this transmission section coming from the host between the transmission sections connected to the rest of the network (second switching state). The control of the switching device takes place from the host: after the host has checked its transmission section for a correct working--the switching device is in said first switching state--it will transmit a control signal ("JOIN" command) to the switching device. Owing to this control signal the switching device switches over to said second switching state, as a result of which the host will be inserted into the network. When the host wants to discontinue its connection to the network, it will transmit for that purpose a control signal to the switching device again, as a result of which this switching device will come into the former state again.
Besides switching devices for connecting a host to the network, the network can also comprise switching devices for effecting a reconfiguration of the network, for example in the event of a disturbance or for the sake of maintenance. These switching devices are then controlled--by means of control signals--for example by one another or by a central device.
In the transmission sections the transmission of the signals takes place substantially in the optical domain: the transmission sections consist of one or more glass fibres, which are connected at both ends to E/O converters, where electric signals are converted into optical signals or vice versa.
In the switching devices the switching of the transmission sections takes place in the electrical domain, in other words, the switching devices are electric as to their nature.
The control signals are transmitted next to the information signals via the same glass fibres. For this purpose "intelligence" is added to said E/O-converters and the control signals and the information signals in the electrical domain are joined by means of multiplexing or separated from one another by means of demultiplexing.
Summarizing it can be stated that the transmission of the control signals and of the information signals takes place (substantially) in the optical domain, whereas on the other hand the switching and the joining respectively the separation of the control signals and the information signals take place in the electrical domain. Because of the fact that the conversion from the optical domain to the electrical domain and vice versa takes place relatively frequently, the network is separated at many places by active (electronic) elements. This (repeated) conversion works restrictively with regard to the sort (of form) and the speed of the information signals to be transmitted via the network; in other words, the conversion restricts the maximum speed of transmission to be reached and the possibilities (freedom) with regard to the sort (e.g. digital, analog, coherent) of those signals. Moreover the known network can transmit only those information signals and control signals for which the conversion devices are suited. Consequently it will be possible to realize future changes with regard to the sort and/or the speed of transmission to a limited degree without adapting or replacing all (!) the conversion devices in the network--if that would be possible--.